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The basic building block of the nervous system.
Neuron
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The cell body of the neuron.
Soma
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to be stimulated by other neurons or by special receptor cells (such as hair cells in the cochlea or vestibular system)
Dendrites basic function
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Act as receiving ends of the nerve cells
Convey nerve impulses into the cell body
Dendrites (2)
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Long and thin extensions of the cell body; convey information away from the cell body
Axon
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The point at which a nerve impulse is passed from the axons of one nerve cell to the dendrites of another nerve cell; the junction of two neurons
Synapse
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A thin white sheath of fatty substances that surrounds the axons of most fibers; acts as an insulator between the positively charged axon and the negatively charged surrounding environment
Myelin sheath
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made up of the brain and spinal cord
Central Nervous System (CNS)
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a collection of nerve cells bodies in the CNS
Nucleus
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Collection of nerve cell bodies that have a common function but lie outside the CNS
Ganglion
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Cell bodies of the neurons that innervate the hair cells of the cochlea
Spiral ganglion of Corti definition
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Found in the modiolus
Spirals with the turns of the cochlea
Spiral ganglion of Corti (2)
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Small openings in the edge of the osseous spiral lamina
Habenula Perforata
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Neurons carry information in one direction; that is, they are unidirectional
Cochlear Innervation
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There are 30,000 or more auditory nerve fibers in humans. ____ of the fibers go to the OHC. At least ____of the fibers go to the IHC.
There are ______ in humans. 10% or fewer of the fibers go to the OHC. At least 90% of the fibers go to the IHC.
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carry information from the hair cells to the brain.
Afferent nerve fibers
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Afferent nerve fibers originating from the IHC
Radial Fibers definition
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compose 95% of the afferent fibers
Primary carriers of sensory information
Any one afferent neuron supplies but one IHC, but any single hair cell is supplied by 8-10 neurons
Radial fibers
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Afferent fibers connected to the OHC
Outer Spiral Fibers definition
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compose 5% of the afferent fibers
One neuron receives input from many OHCs; or, said another way, many OHCs share one neuron
Outer spiral fibers
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carry information from the brain to the hair cells
Efferent nerve fibers
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Efferent fibers connected to the OHC
Tunnel Radial Fibers definition
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Controls cochlear amplifier
Innervation is denser at the base of the cochlea
Tunnel Radial Fibers (2)
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Efferent fibers that connect to the IHC
Inner Spiral Fibers: Inhibition of afferent fibers
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Arranged with respect to frequency
Tonotopic organization
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Neurons carrying _______ information located on the outside of auditory nerve; neurons carrying ________ information are located in the center
Neurons carrying high frequency information located on the __________; neurons carrying low frequency information are located ______.
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Central Auditory Pathway
- Brainstem
- Diencephalon
- Cortex
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_________
The medulla, which is continuous with the spiral ganglia
The pons, which is above the medulla
The midbrain, which is above the pons
Brainstem
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____________
Located above the midbrain and is surrounded by the cerebral hemisphere
Contains the Thalamus
Diencephalon
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________
Is made up of two cerebral hemispheres
Each hemisphere contains four lobes: Frontal, Parietal, Occipital, Temporal
Cortex
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1st Order: Auditory Nerve to Cochlear nucleus
- VIII cranial nerve contains both auditory and vestibular fibers.
- Travels from the cochlea to the brainstem via the internal auditory meatus
- Joins the brainstem at the cerebellopontine angle
- Fibers then travel ipsilaterally to the Cochlear Nucleus located in the medulla where they synapseNerve TrunkNerve bundleNeuron with myelin sheath
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2nd Order: CN to Superior Olivary Complex
- Approx. 2/3rds of the fibers decussate after leaving the CN and travel to the SOC on the contralateral side where they synapse
- The remaining 1/3rd of the fibers ascend to the SOC on the ipsilateral side where they synapse
- Binaural information is first available at the SOC, which is important for localization
- The SOC is also located in the medulla
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3rd Order: SOC to Nucleus of the Lateral Lemniscus
- The fibers ascend ipsilaterally and contralaterally from the SOC to the NLL where they synapse
- NLL is located in the pons
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4th Order: NLL to Inferior Colliculus
- The fibers ascend ipsilaterally and contralaterally from the NLL to the IC where they synapse
- The two inferior colliculi are connected by fibers allowing a crossover of information from one side of the brainstem to the other
- The IC is located in the midbrain
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5th Order: IC to Medial Geniculate
- The fibers ascend ipsilaterally from the IC to the Medial Geniculate, where they synapse
- The MG is located in the Thalamus
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6th Order: MG to Cortex
The fibers ascend ipsilaterally to the auditory cortex in the temporal lobe, at the anterior transverse temporal gyrus (Herschel’s gyrus), where they synapse
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Descending Auditory Pathway: Efferent fibers
- Essentially same structures as afferent pathways, but in reverse order
- Outer hair cells more often the destination
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From the SOC upward, ______ contain information from both ears
First point where hearing from both ears is represented is___.
The SOC is responsible for the ability to______.
_______ is present at each nucleus
- _________ , both ipsi and contra tracts contain information from both ears
- First point where hearing from both ears is represented is the SOC
- The SOC is responsible for the ability to localize sounds in space
- Tonotopic organization is present_____.
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Peripheral Nervous System
- Cranial Nerves
- Spinal Nerves
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Cranial Nerves
- Twelve pairs identified by a roman numeral and a name, ordered from top to bottom of the brainstem.
- Name may reflect function, structure, or distribution
- Nerve is an aggregate of neuron fibers
- Nerves may be afferent or efferent; most are both
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Twelve Cranial Nerves
Which are important for speech?
- Trigeminal
- Facial
- Glossopharyngeal
- Vagus
- Accessory
- Hypoglossal
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V. Trigeminal Nerve
- Largest cranial nerve
- Sensory portion (afferent)
- face
- mouth
- lower jaw
- Motor portion (efferent)
- muscles of mastication
- velum
- mylohyoid and anterior belly of digastric
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VII. Facial
- Large and complex
- Facial nerve proper--efferent
- Nervous intermedius--both efferent and afferent
- Communicates w/ other cranial nerves
- Trigeminal
- Vagus
- Glossopharyngeal
- Cervical
- Muscles of facial expression, from above the eye to lower jaw
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IX. Glossopharyngeal
- Both sensory and motor
- Supplies the tongue and pharynx
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X. Vagus
- “Wandering Course”: large distribution of nerves
- Both afferent and efferent courses
- Serves large array of structures:
- Larynx
- Pericardium
- Stomach
- Pancreas
- Spleen
- Kidneys
- Intestines
- Liver
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XI. Accessory
- Partly cranial and partly spinal
- Interacts with vagus nerve
- Serves: Larynx, Sternocleidomastoid, Trapezius muscles
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XII. Hypoglossal
- Primarily motor
- Supplies: Intrinsic tongue muscle
- Extrinsic tongue muscles
- Strap muscles
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